Solar-Metallicity Gas in the Extended Halo of a Galaxy at $z\sim 0.12$

Abstract

We present the detection and analysis of a weak low-ionization absorber at $z=0.12122$ along the blazar sightline PG~$1424+240$, using spectroscopic data from both $HST$/COS and STIS. The absorber is a weak Mg II analogue, with incidence of weak C II and Si II, along with multi-component C IV and O VI. The low ions are tracing a dense ($n_H\sim 10^{-3}$ cm${}^{-3}$) parsec scale cloud of solar or higher metallicity. The kinematically coincident higher ions are either from a more diffuse ($n_H\sim 10^{-5}-10^{-4}$ cm${}^{-3}$) photoionized phase of kiloparsec scale dimensions, or are tracing a warm (T $\sim 2\times 10^5$ K) collisionally ionized transition temperature plasma layer. The absorber resides in a galaxy overdense region, with 18 luminous ($>L^{\ast }$) galaxies within a projected radius of $5$ Mpc and $750$ km s${}^{-1}$ of the absorber. The multi-phase properties, high metallicity and proximity to a $1.4$ $L^{\ast }$ galaxy, at $\ddot{I}\sim 200$ kpc and $|\hat{I}”v|=11$ km s${}^{-1}$ separation, favors the possibility of the absorption tracing circumgalactic gas. The absorber serves as an example of weak Mg II - O VI systems as a means to study multiphase high velocity clouds in external galaxies.

17 pages, 8 figures, 3 tables. Accepted for publication in MNRAS